build: downloader: silently ignores errors in some cases

Brief Description
-----------------

Downloader silently ignores errors while downloading source packages in some cases. See logs below.

Severity
--------
Major

Steps to Reproduce
------------------
Difficult to reproduce - see logs below

Expected Behavior
------------------
Download errors must result in "downloader" exiting with a non-zero status

Actual Behavior
----------------
Downloader exits with 0 even if some downloads failed.

Reproducibility
---------------
Seen once

System Configuration
--------------------
N/A

Branch/Pull Time/Commit
-----------------------
master/2023-10-13

Last Pass
---------
N/A

Timestamp/Logs
--------------

11:37:21 2023-10-13 15:37:21,658 - debrepack - INFO: [ Run - "dget -d http://mirror.starlingx.cengn.ca:80/mirror/debian/snapshot.debian.org/archive/debian/20230927T030735Z/pool/main/l/lldpd/lldpd_1.0.11-1+deb11u2.dsc" ]
11:37:25 2023-10-13 15:37:24,874 - debrepack - DEBUG: stdout: dget: retrieving http://mirror.starlingx.cengn.ca:80/mirror/debian/snapshot.debian.org/archive/debian/20230927T030735Z/pool/main/l/lldpd/lldpd_1.0.11-1+deb11u2.dsc
11:37:25 2023-10-13 15:37:24,875 - debrepack - DEBUG: stdout: dget: using existing lldpd_1.0.11.orig.tar.gz
11:37:25 2023-10-13 15:37:24,875 - debrepack - DEBUG: stdout: dget: using existing lldpd_1.0.11.orig.tar.gz.asc
11:37:25 2023-10-13 15:37:24,875 - debrepack - DEBUG: stdout: dget: retrieving http://mirror.starlingx.cengn.ca:80/mirror/debian/snapshot.debian.org/archive/debian/20230927T030735Z/pool/main/l/lldpd/lldpd_1.0.11-1+deb11u2.debian.tar.xz
11:37:25 2023-10-13 15:37:24,875 - debrepack - DEBUG: stdout: lldpd_1.0.11-1+deb11u2.dsc:
11:37:25 2023-10-13 15:37:24,875 - debrepack - DEBUG: stdout: Good signature found
11:37:25 2023-10-13 15:37:24,875 - debrepack - DEBUG: stdout: validating lldpd_1.0.11.orig.tar.gz
11:37:25 2023-10-13 15:37:24,875 - debrepack - DEBUG: stdout: validating lldpd_1.0.11.orig.tar.gz.asc
11:37:25 2023-10-13 15:37:24,875 - debrepack - DEBUG: stdout: All files validated successfully.
11:37:25 2023-10-13 15:37:24,875 - debrepack - DEBUG: stderr: % Total % Received % Xferd Average Speed Time Time Time Current
11:37:25 2023-10-13 15:37:24,876 - debrepack - DEBUG: stderr: Dload Upload Total Spent Left Speed
11:37:25 2023-10-13 15:37:24,876 - debrepack - DEBUG: stderr: 0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0
11:37:25 2023-10-13 15:37:24,876 - debrepack - DEBUG: stderr: 0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0
11:37:25 2023-10-13 15:37:24,876 - debrepack - DEBUG: stderr: 0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0
11:37:25 2023-10-13 15:37:24,876 - debrepack - DEBUG: stderr: 100 2473 100 2473 0 0 4639 0 --:--:-- --:--:-- --:--:-- 10991
11:37:25 2023-10-13 15:37:24,876 - debrepack - DEBUG: stderr: % Total % Received % Xferd Average Speed Time Time Time Current
11:37:25 2023-10-13 15:37:24,876 - debrepack - DEBUG: stderr: Dload Upload Total Spent Left Speed
11:37:25 2023-10-13 15:37:24,876 - debrepack - DEBUG: stderr: 0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0
11:37:25 2023-10-13 15:37:24,876 - debrepack - DEBUG: stderr: 0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0
11:37:25 2023-10-13 15:37:24,876 - debrepack - DEBUG: stderr: 0 0 0 0 0 0 0 0 --:--:-- --:--:-- --:--:-- 0
11:37:25 2023-10-13 15:37:24,876 - debrepack - DEBUG: stderr: curl: (22) The requested URL returned error: 404 Not Found
11:37:25 2023-10-13 15:37:24,876 - debrepack - DEBUG: stderr: dget: curl lldpd_1.0.11-1+deb11u2.debian.tar.xz http://mirror.starlingx.cengn.ca:80/mirror/debian/snapshot.debian.org/archive/debian/20230927T030735Z/pool/main/l/lldpd/lldpd_1.0.11-1+deb11u2.debian.tar.xz failed
11:37:25 2023-10-13 15:37:24,877 - debrepack - DEBUG: stderr: skipping lldpd_1.0.11-1+deb11u2.debian.tar.xz (not present)

===========================
This download failed: ttp://mirror.starlingx.cengn.ca:80/mirror/debian/snapshot.debian.org/archive/debian/20230927T030735Z/pool/main/l/lldpd/lldpd_1.0.11-1+deb11u2.debian.tar.xz , yet the script returned 0. This caused build errors down the pipeline.

Note: this file is no longer missing on starlingx mirror

Test Activity
-------------
N/A

Workaround
----------
N/A